It is known to coat medical devices, e.g. catheters for introduction into human cavities such as blood vessels, digestive organs and the urinary system, with a hydrophilic coating, at least on the surface of the insertable part which is introduced or comes into contact with mucous membranes, etc., during introduction of the device. An advantage with such a hydrophilic coating is that it becomes extremely slippery when it is swelled with water, preferably immediately before introduction into the human body and thus ensures a substantially painless introduction with a minimum of damage on tissue.
A large number of methods are known for the production of hydrophilic surface coatings. These methods are mainly based on the fact that the substrate to be provided with a hydrophilic surface coating, in the course of one or more process stages with intermediary drying and curing, is coated with one or more layers, which are brought to react with one another in various ways, e.g. by polymerisation initiated by irradiation, by graft polymerisation, by the formation of interpolymeric network structures, or by direct chemical reaction. A known hydrophilic coating process is e.g. disclosed in EP 0 093 093, where isocyanate is used to form a polyurea network for connecting hydrophilic PVP to the substrate. Further, EP 0 217 771 describes a method of adding an osmolality increasing compound to such a hydrophilic coating in order to improve the water retention properties and low friction of the coating. Further, WO 98/58989 discloses a hydrophilic coating which is cross-linked by means of irradiation, and incorporating a water soluble osmolality increasing compound therein.
The total production process for medical devices with hydrophilic coatings is consequently relatively complex and cumbersome. A suitable substrate should be provided, a hydrophilic coating should be arranged on the substrate, which normally involves a number of timely separated steps, the medical device should be enclosed in a suitable package, and be sterilized, e.g. by means of irradiation or ethylene oxide gas. Due to the large number of steps required for the production, the production takes long time, and is relatively costly.
Accordingly, there is a need for a more time and cost effective production method for medical devices with a hydrophilic coating, while still maintaining adequate adhesion to the substrate, as well as good water retention and low friction properties, and preferably also maintaining biocompatibility to human tissue such as mucous membrane.